The present disclosure relates to a sound output apparatus, and more particularly, to a sound output apparatus capable of enhancing output characteristics in audible frequency bands including low-frequency bands and high-frequency bands.
In general, a piezoelectric device refers to a device having a characteristic capable of mutually changing electrical energy to/from mechanical energy. That is, an electric voltage is generated when a pressure is applied on the piezoelectric device (the piezoelectric effect), and an increase or decrease in volume or length due to an internal pressure change occurs when the electric voltage is applied thereto (the inverse piezoelectric effect). The piezoelectric device is configured with a piezoelectric layer and an electrode provided thereon, and a pressure thereof changes according to the electrical voltage applied to the piezoelectric layer through the electrode.
Various components such as a piezoelectric speaker, a vibration apparatus, or the like may be manufactured using the piezoelectric device. Among these, the piezoelectric speaker is a component which acoustically converts mechanical movements of the piezoelectric device into a sound in desired frequency bands using a vibration plate. It is advantageous that the piezoelectric speaker is thinner and lighter, and smaller in power consumption than an existing dynamic speaker, and thus the piezoelectric speaker can be used in electronic apparatuses such as smart phones which are required to be small, thin, and light-weighted. However, the piezoelectric speaker is disadvantageous in that the piezoelectric speaker delivers strong high-pitched sound and weak low-pitched sound, which causes a user to be unable to listen to music for a long time.
Meanwhile, dynamic speakers are widely used for music playback. The dynamic speakers use the principle that when an audio signal current is applied to a voice coil placed within the magnetic field of a magnet, a mechanical force acts on the voice coil according to the intensity of the current, and thus a movement is caused. However, the dynamic speakers are suitable for implementing low-frequency sound, but are relatively poor for implementing high-frequency sound, and thus the dynamic speakers have limitations in providing high sound quality.